Understanding the molecular basis and functional consequences of alterations in cell-surface components involved in the intercellular interactions of epithelial cells has been the long term goal of this project. In this revised proposal, we have focused our investigations on the characterization of cell-CAM 105, a 110 kD glycoprotein which is thought to play a role in the adhesive interactions of adult rat hepatocytes (ARH). Based on data obtained from our research and observations made in other laboratories, we are proposing that ell-CAM 105 plays a central role in the formation of the bile canalicular domain of rat hepatocytes and further that decreased expression of this molecule observed on primary tumors is closely linked to the loss of histotypic organization. Experiments to test these hypotheses have been organized around a working model which incorporates our current knowledge of the structure, function and expression of cell-CAM 105. Specific Aim 1 will be directed at examining the formation and distribution of the high and low molecular weight and the phosphorylated forms of cell-CAM 105 and the association during contact formation of these various forms with themselves or with a 65/67 kD calcium binding protein. Specific Aim 2 will focus on determining the expression and localization of cell-CAM 105 during bile canalicular formation. Emphasis will be placed on obtaining circumstantial (temporal relationships) and direct (inhibition by cell-CAM 105 specific antibodies) evidence for as causative relationship between relocalization and expression of cell-CAM 105 and bile canalicular formation. Bile canalicular domains will be examined in vitro in primary cultures of hepatocytes maintained in the presence of DMSO and in vivo during liver regeneration and during ethionine or DENA induced carcinogenesis. Specific Aim 3 will examine factors which modulate the domain specific localization and expression of cell-CAM 105. Factors to be examined factors which modulate hormonally defined medium, addition of DMSO during contract formation, growth on substrata that allow free access to basolateral surfaces and primary cultures derived from intact tissue sections. Specific Aim 4 will be devoted to the isolation of a full length cDNA clone for cell-CAM 105 which can be used to gain further insight into the structure, function and expression of cell-CAM 105 in normal liver and changes in expression during carcinogenesis. These studies will provide new insight into molecular events involved in the formation of histotypic interactions and changes in these events that lead to the aberrant interactions characteristic of malignant cells.